1. Field of the Invention
This invention relates to a color pick-up tube face plate for use in a color television camera composed of one or two pick-up tubes. Usually television cameras of this type are referred to as single-tube color television cameras and two-tube color television cameras. The pick-up tube used in these cameras is referred to as the single pick-up tube for color television and is hereinafter simply called the color pick-up tube.
2. Description of the Prior Art
In a conventional face plate of a color pick-up tube a large number of stripe-shaped red-transmitting, green-transmitting and blue-transmitting filters are periodically distributed adjacent one another on a surface of a transparent substrate, and stripe-shaped transparent conductive films are deposited on these stripe-shaped filters. Furthermore, a photoconductive film is deposited on the whole surface of the stripe-shaped transparent conductive films and exposed portions of the transparent substrate.
For the face plate of a color pick-up tube, two kinds of stripe-shaped filters are used.
One of them is the so called interference filter. This filter is composed of layers, of inorganic films such as cerium oxide, magnesium fluoride, silicon dioxide or titanium oxide.
The other stripe-shaped filter is the so called gelatin filter, and is composed of a gelatin film containing various pigments.
In order to form these stripe-shaped interference filters on the surface of the transparent substrate, the so-called lift-off method has been employed. This is a method to form suitable films in the desired shapes or patterns on the substrate. According to this method, first of all, soluble material films having shapes or patterns inverted to said desired shapes or patterns are deposited on the surface of the substrate. Suitable film is deposited on the whole surface of said substrate containing said soluble material films.
Then, the soluble films are subjected to the dissolution procedure using solvent fit for said soluble material, thereby all of the soluble material films are perfectly removed. Also, as a result of the dissolution of the soluble films, the portion of the suitable films deposited on the soluble films are removed from the substrate, so that the required films having the desired pattern remained on the surface of the substrate.
However, in the lift-off method, removal of undesired portions of the suitable films follows dissolution of the soluble films, so that the edges of the stripe-shaped filters 11, 12, 13 formed on the substrate 1 are roughened remarkably as shown in FIG. 1. Therefore, so long as the conventional lift-off method is employed, it is very difficult to form stripe-shaped interference filters having favorable straight edges.
Although a great part of the light incidented upon the roughened edges of the stripe-shaped filters can transmit these edges, a considerable part of the incident light is reflected or scattered by these roughened edges and consequently the direction of the light is greatly diverted.
On the other hand, the stripe-shaped gelatin filters having the favorable straight edges can be formed very exactly and very easily. However, the light transmitted around the boundary portions of each filter contains two different colors of adjoining stripe-shaped filters. Particularly when the light is incidented upon the face plate at angle, such a color mixture phenomenon takes place very remarkably. For this reason, a favorable picture having good color uniformity and purity cannot be obtained with the conventional color pick-up tube.